Light-emitting diodes (LEDs) have a wide range of applications in industry. An LED is typically composed of a semiconductor die mounted on a header that provides mechanical support for and electrical connections to the semiconductor die. The semiconductor die is then encapsulated to protect it. The encapsulation is transparent or includes a transparent window to allow light generated by the semiconductor die to be emitted. The header and the encapsulation collectively constitute the package of the LED.
Parameters used to characterize the performance of an LED include brightness and radiant power. Another important parameter used to characterize the performance of an LED is the radiation pattern, i.e., the dependence of brightness on angle relative to the optical axis of the LED. The semiconductor die emits light in a substantially isotropic radiation pattern, which is suitable for relatively few applications. Typical LEDs include a converging element that includes a convex surface to generate a specific radiation pattern from the isotropic radiation pattern of the semiconductor die. Examples of such converging elements include a convex spherical or aspherical lens and encapsulation that includes a convex surface facing the semiconductor die.
Different applications use LEDs with different radiation patterns. For example, an LED configured for use in back lighting for an LCD screen has a relatively wide and uniformly-spread radiation pattern, whereas an LED configured for use in a signal light, such as a traffic light, has a relatively narrow radiation pattern and a high intensity. An LED configured for use in a position or rotation encoder has a collimated or point source radiation pattern.
The need to provide LEDs configured for many different applications that require different radiation patterns cause manufacturers of LEDs to use a large number of different types of LED package, each with its own shape. The need to keep an inventory of many types of package to meet customers' demands contributes to the manufacturing cost of LEDs. Since manufacturers are under constant pressure to reduce costs, what is needed is an LED that can easily be manufactured with a range of different radiation patterns without the need to keep an inventory of many different types of package. What is also needed is a way to manufacture such LEDs.